1.not tense or tautslack and wrinkled skinslack sailsa slack rope2.lacking in strength or firmness or resiliencea slack grip3.flowing with little speed as e.g. at the turning of the tideslack water4.lacking in rigor or strictnessslack in maintaining discipline

'slack' - used as a noun5.dust consisting of a mixture of small coal fragments and coal dust and dirt that sifts out when coal is passed over a sieve6.a noticeable deterioration in performance or qualitya gradual slack in output7.a stretch of water without current or movementsuddenly they were in a slack and the water was motionless8.a soft wet area of low-lying land that sinks underfoot9.the condition of being loose (not taut)10.a cord or rope or cable that is hanging looselyhe took up the slack

'slack' - used as a verb11.avoid responsibilities and work, be idle12.be inattentive to, or neglectHe slacks his attention13.release tension onslack the rope14.make less active or fast15.become slow or slower16.make less active or intense17.become less in amount or intensity18.cause to heat and crumble by treatment with waterslack lime